Interest in continuously variable hydrostatic transmissions has been increasing in recent years because of the potential operational efficiencies and economies that are increasingly becoming possible in vehicles and other powered systems wherein rotary input power is to be converted to output power at the desired output torque and speed. Examples of continuously variable transmissions that make such efficiencies and economies possible can be found in the following U.S. Patent Applications and Patents:
U.S. Pat. No. 5,423,183 entitled "Hydraulic Machine with Wedge-Shaped Swashplate" issued on Jun. 13, 1995 to Lawrence R. Folsom.
U.S. Pat. No. 5,630,318 entitled "Method of Pumping with a Vane-Type Pump Having a Flexible Cam Ring" issued on May 20, 1997 to Lawrence R. Folsom and Clive Tucker.
U.S. patent application Ser. No. 09/023,653 entitled "Concentric Radial Piston Transmission" filed on Feb. 8, 1998 by Lawrence R. Folsom and Clive Tucker.
U.S. patent application Ser. No. 09/058,719 entitled "Concentric Axial Piston Transmission" filed on Apr. 10, 1998 by Lawrence R. Folsom and Clive Tucker.
The devices shown in these patents and patent applications constitute a significant improvement over the prior art and an evolving progressive improvement among themselves. They provide operational efficiencies and economies in the vehicle superior to any known transmission, and do so in packages that are smaller and lighter weight than other available transmissions.
However, conventional prior art hydrostatic transmissions are known by experts in the art to be noisy and inefficient. Convincing those experts and vehicle manufacturers that these new generation hydrostatic transmissions have overcome the intractable problems of the prior art is difficult. Therefore, additional improvements would facilitate acceptance of the new generation hydrostatic transmissions.
One such improvement would be in the area of leakage from rotating interfaces, particularly those where working fluid is commutated between the differentially rotating pump and motor.
Another improvement would be in the area of dynamic balancing. The difficulty of balancing rotating equipment to preclude vibration induced by rotating eccentric masses becomes worse exponentially with increasing speed of rotation.
Yet another improvement would be in reducing the losses caused by "windage" and fluid drag associated with the rotating elements inside the transmission housing. In applications having a prime mover with a high rotating speed, such as an electric motor, turbine engine or high performance spark ignition gasoline engine, the input elements would rotate at the prime mover output speed unless a gear reduction unit were interposed between the prime mover and the transmission. Gear reduction units add undesirable cost and weight. The windage and fluid drag losses can be greatly reduced by reducing the speed of rotation of those rotating elements.
One approach for achieving these improvements is shown in a U.S. Provisional application Ser. No. 60/065,377 filed on Nov. 12, 1997 by Folsom and Tucker entitled "Serial Bent Axis Apparatus". It would be desirable to use this approach or a variation thereof, in a concentric hydrostatic transmission in situations requiring more axial compactness, such as motor scooters, motor cycles, RV's and snowmobiles.